1. Field of the Invention
This invention relates to an integrated photo sensor provided by integrating a light-receiving element and elements for a signal processing circuit on a semiconductor substrate.
2. Description of the Related Art
JP-A-10-289994 proposes an integrated photo sensor. The photo sensor has a light-receiving element and signal processing circuit elements that are integrated on one chip, and a shading film for selectively determining a light-receiving region on the chip surface. It is considered that this structure reduces the chip size as small as possible for the integration, and prevents erroneous operations of the signal processing circuit elements ascribed to light incident on the elements. This kind of sensor is generally covered with a protective film made of resin such as silicone gel or the like for protection.
Specifically, the shading film covers a region other than the light-receiving element, and an insulating film (intermediate insulating film) such as a silicon oxide film underlies the shading film to assure electrical insulation from each of the signal processing circuit elements (each element for a digital circuit, an analog circuit, adjustment, or the like).
If the intermediate insulating film exists on the light-receiving element, however, optical characteristics vary due to interference of light in accordance with wavelength of light. To prevent this variation in optical characteristics, the intermediate insulating film is removed not to exist on the light-receiving element. The removal of the intermediate insulating film, however, increases the manufacturing cost. In addition, in this case, a protective film is disposed on the light-receiving element, which can vary sensor sensitivity.
JP-A-8-32045 discloses another integrated photo sensor. In the photo sensor, an intermediate insulating film remains on a light-receiving element. Further, a film (an oxide film formed by plasma CVD, and hereinafter referred to as a P--SiO.sub.2 film) having a refractive index close to that of the intermediate insulating film is disposed on the intermediate insulating film provided on the light-receiving element so that light is restricted from being reflected at the interface between the P--SiO.sub.2 film and the intermediate insulating film.
In this structure, since the thickness of the P--SiO.sub.2 is thin, the reflection of light at the interface can be prevented effectively as compared to a case where a SiN film having a largely differing refractive index is left on the light-receiving element. However, since it is difficult to eliminate the effects by interference, the variation in optical characteristics is not prevented sufficiently.